Related Field
The present invention relates to transmitter and receivers geometries and associated communications systems and methods, particularly but not exclusively for use in multiple-input multiple-output optical communications systems.
Description of Related Art
Visible light communication (VLC) is being contemplated as a method of transmitting high data rates to mobile devices. VLC can also replace point-to-point infrastructure in places where conventional infrastructure does not exist or is too expensive to build. This technique could overcome the soon to be reached limitations in the availability of sufficient capacity in the radio spectrum to fulfil the growing demand. One of the protocols for VLC takes advantage of multiple transmitters and receivers in a so called multiple-input multiple-output (MIMO) arrangement, and separates the transmitted channels in space.
In MIMO systems commonly used in optical communications, each transmitter-receiver couple should form a distinct communication channel. In this way, it is possible for the system to distinguish between different simultaneously transmitted data streams.
It can be more difficult to achieve this requirement in optical communications systems, such as VLC systems, than in traditional radio frequency based systems, since the variability of the channel in optical communications systems is a lot less than for radio frequency based systems. In addition, since light beams become more parallel as the separation between the transmitter and receiver increases, the channel conditions become more similar at greater transmitter-receiver separations.
One option for overcoming this problem is to increase the separation of different transmitters and/or different receivers. However, this approach can lead to increases in the size of the transmitter and/or receiver systems, which may be undesirable.